Rotational coupling device

ABSTRACT

A rotational coupling device for use as a clutch and/or brake is provided having improved magnetic efficiency and structural integrity. An electrical conduction assembly is disposed within a field shell between radially spaced inner and outer poles of the field shell. The assembly includes a conductor disposed within a shell having a radially extending flange that is disposed proximate the outer pole of the field shell and that is affixed to the field shell at a plurality of points.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to rotational coupling devices such as brakes andclutches and, in particular, to a rotational coupling device havingimproved magnetic efficiency and performance and improved structuralcharacteristics.

2. Discussion of Related Art

Rotational coupling devices such as clutches and brakes are used tocontrol transfer of torque between rotational bodies. One type ofconventional device is illustrated in U.S. Pat. Nos. 5,119,918,5,285,882 and 5,971,121, the entire disclosures of which areincorporated herein by reference. This device includes a rotor that iscoupled to an input shaft for rotation with the input shaft about arotational axis. A field shell is also disposed about the input shaft onone side of the rotor and is fixed against rotation. The field shelldefines radially spaced, axially extending inner and outer poles betweenwhich an electrical conductor is disposed, facing the rotor. A brakeplate is coupled to the field shell and axially spaced from the fieldshell. The brake plate is disposed on a side of the rotor opposite theconductor. An armature coupled to an output member is disposed on thesame side of the rotor as the brake plate and is disposed axiallybetween the rotor and the brake plate. The armature is coupled to anoutput member by a plurality of leaf springs. Energizing the conductorproduces a magnetic circuit in the field shell, rotor and armature thatdraws the armature into engagement with the rotor and couples the inputshaft and output member together for rotation. Upon deenergization ofthe conductor, the leaf springs draw the armature out of engagement withthe rotor and into engagement with the brake plate to brake the armatureand output member. Permanent magnets coupled to the brake plate are alsoused to create another magnetic circuit between the brake plate, thefield shell and the armature to assist the leaf springs in braking thearmature and output member.

The above described devices generally perform well. The magneticcircuits within the device, however, are not optimally efficient orisolated from each other. Further, the armature is difficult todisengage from the brake plate and the engagement surfaces of the devicestill suffer from an undesirable amount of wear. The mounting of theconductor within the field shell of the device is also not optimal andthere is a desire to improve the strength of the mounting arrangement.

The inventors herein have recognized a need for a rotational couplingdevice that will minimize and/or eliminate one or more of theabove-identified deficiencies.

SUMMARY OF THE INVENTION

The present invention provides a rotational coupling device.

A rotational coupling device in accordance with one aspect of thepresent invention includes a rotor coupled to an input shaft forrotation therewith. The input shaft is disposed about a rotational axis.The device further includes a field shell disposed about the input shaftand fixed against rotation. The field shell defines axially extending,radially spaced inner and outer poles. The device further includes anelectrical conduction assembly disposed within the field shell betweenthe inner and outer poles and on a first side of the rotor. The assemblyincludes a conductor disposed within a shell. The shell includes aradially outwardly extending flange disposed proximate the outer pole ofthe field shell. The device further includes an armature disposedaxially between the rotor and the brake plate on a second side of therotor opposite the conductor. The armature is coupled to an outputmember. The flange of the conductor shell is affixed to the field shellat a plurality of points.

A rotational coupling device in accordance with the present inventionrepresents an improvement over conventional devices because theconduction assembly is better secured to the field shell. In particular,connection of the conduction assembly at the radially outer diameter ofthe field shell enables a greater number of connections at a largerradius than in conventional devices in which the conduction assembly isconnected to the field shell proximate the inner diameter of the fieldshell thereby increasing resistance to torsional vibration. Further, theconnection facilitates an improved structural arrangement in which theinner pole of the rotor is disposed radially outwardly of the inner poleof the field shell for a more efficient magnetic circuit.

These and other advantages of this invention will become apparent to oneskilled in the art from the following detailed description and theaccompanying drawings illustrating features of this invention by way ofexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a rotational coupling device in accordance withone embodiment of the present invention.

FIG. 2 is a cross-sectional view of the rotational coupling device ofFIG. 1.

FIG. 3 is an enlarged cross-sectional view of a portion of therotational coupling device of FIGS. 1-2 illustrating another aspect ofthe present invention.

FIG. 4 is an enlarged cross-sectional view of a portion of a rotationalcoupling device in accordance with another embodiment of the presentinvention.

FIG. 5 is an enlarged cross-sectional view of a portion of a rotationalcoupling device in accordance with another embodiment of the presentinvention.

FIG. 6 is an enlarged cross-sectional view of a portion of a rotationalcoupling device in accordance with another embodiment of the presentinvention.

FIG. 7 is an enlarged view of a portion of FIG. 2.

FIG. 8 is a plan view of a rotational coupling device in accordance withanother embodiment of the present invention.

FIG. 9 is an enlarged cross-sectional view of a portion of therotational coupling device of FIG. 8.

FIG. 10 is a plan view of a rotational coupling device in accordancewith another embodiment of the present invention.

FIG. 11 is an enlarged cross-sectional view of a portion of therotational coupling device of FIG. 10 taken along lines 11-11.

FIG. 12 is an enlarged cross-sectional view of a portion of a rotationalcoupling device in accordance with another embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIGS. 1-2illustrates a rotational coupling device 20 in accordance with oneembodiment of the present invention. Device 20 functions as a clutch toselectively transfer torque from an input shaft 22 to an output member24. Device 20 also functions as a brake on output member 24 when torqueis not being transferred to output member 24. Device 20 may be providedfor use in a riding lawnmower or similar device. It will be understoodby those of ordinary skill in the art, however, that device 20 may beused in a wide variety of applications requiring a clutch or brake.Device 20 may include a spacer 26, a rotor 28, a field shell 30, anelectrical conduction assembly 32, a brake plate 34, an armature 36 andone or more permanent magnets 38.

Input shaft 22 provides a source of torque for driving output member 24.Shaft 22 may be made from conventional metals and metal alloys and maybe solid or tubular. Shaft 22 is centered about a rotational axis 40 andis driven by an engine, electric motor or other conventional powersource. In the illustrated embodiment input shaft 22 is inserted intodevice 20 on a side of device 20 opposite output member 24. It should beunderstood, however, that the orientation of input shaft 22 and spacer26 could be reversed such that input shaft 22 is inserted into device 20on the same side as output member 24.

Output member 24 transfers torque to a driven device such as a lawnmowerblade. Member 24 may comprise a conventional pulley around which atorque transmitting belt is wound and coupled to the driven device.

Spacer 26 is provided to support output member 24 in assembled relationwith the other components of device 20 and may be made from conventionalmaterials including powdered metals. Spacer 26 is disposed about axis 40and is generally cylindrical in shape. Spacer 26 has a generallycylindrical outer surface that may include a keyway configured toreceive a key of rotor 28. Spacer 26 also defines a flange 42 at oneaxial end.

Rotor 28 is provided for selective engagement with armature 36 totransmit torque between input shaft 22 and output member 24. Rotor 28 isdisposed about axis 40 and is coupled to input shaft 22 for rotationtherewith. Rotor 28 may be made from conventional metals and metalalloys and includes a hub 44 and a rotor disc 46.

Hub 44 is tubular and includes a radially inwardly extending key 48configured to be received within the keyways of input shaft 22 andspacer 26. Proximate its radially inner diameter and at either axialend, hub 44 supports bearings 50, 52. At its radially outer diameter,hub 44 defines an axially extending inner rotor pole 54. Hub 44 furtherdefines an axially extending recess 56 radially inwardly of pole 54 fora purpose described hereinbelow.

Disc 46 extends radially outwardly from hub 44. Disc 46 is coupled tohub 44 through, for example, a press-fit relationship includingplurality of complementary lugs and notches. As is known in the art,disc 46 may include a plurality of radially spaced rows of angularlyspaced, banana shaped slots 58. Upon energization of conduction assembly32, slots 58 cause magnetic flux to travel back an forth between disc 46and armature 36 across an air gap enabling a high torque engagementbetween rotor 28 and armature 36. In the illustrated embodiment, disc 46includes three rows of slots 58. It should be understood, however, thatthe number of rows of slots 58, the number of slots 58 in any one row,and the size and shape of slots 58 may vary. At its outer diameter, disc46 defines an axially extending outer rotor pole 60. Pole 60 is radiallyaligned with pole 54 and spaced radially outwardly of pole 54.

Field shell 30 is provided to house conduction assembly 32. Shell 30also forms part of a magnetic circuit that causes the selectiveengagement of rotor 28 and armature 36. Field shell 30 may be made fromconventional metals and metal alloys, including steel. Shell 30 iscylindrical and is disposed about axis 40. Shell 30 is fixed againstrotation through, for example, a fastener (not shown) extending througha slot 62 in shell 30. Shell 30 is generally U-shaped in cross-sectionand includes radially inner and radially outer annular members 64, 66.

Inner member 64 is supported on an outer race of bearing 50. Member 64is generally L-shaped in cross-section and defines an axially extendinginner pole 68. Pole 68 extends into recess 56 of hub 44 of rotor 28 andis disposed radially inwardly of inner rotor pole 54 in accordance withone aspect of the present invention described in greater detailhereinbelow.

Outer member 66 is coupled to and supported on inner member 64. Outermember 66 defines an end wall 70, an axially extending outer pole 72,and a flange 74. End wall 70 extends radially outwardly from member 64and defines one or more recesses 76 for a purpose described hereinbelow.Pole 72 is integral with, and extends axially from, end wall 70. Pole 72is disposed radially outwardly of pole 60 of rotor 28. Referring to FIG.3, a radially inner surface of pole 72 may define a stepped innerdiameter forming a shoulder 78 for a purpose described hereinbelow. Anaperture 80 is also formed through pole 72 through which leads forconduction assembly 32 extend outward. Flange 74 is integral with, andextends radially outwardly from, pole 72 at an end of pole 72 oppositeend wall 70. Referring to FIG. 1, flange 74 extends along at least aportion of the circumference of pole 72.

Conduction assembly 32 is provided to create a magnetic circuit amongrotor 28, a spacer 82 (or spacer 26 if the orientation of input shaft 22is reversed), field shell 30, and armature 36 to cause movement ofarmature 36 into engagement with rotor 28 and transmission of torquefrom input shaft 22 to output member 24. Conduction assembly 32 isgenerally annular and is disposed about axis 40 within field shell 30.In particular, assembly 32 is disposed between the inner and outer poles68, 72 of shell 30. Assembly 32 includes a conductor 84 and a shell 86.

Conductor 84 may comprise a conventional copper coil although otherknown conductors may alternatively be used. Conductor 84 may beconnected electrically to a power supply (not shown) such as a battery.Upon energization of conductor 84, a magnetic circuit is formed betweenrotor 28, a spacer 82 (or spacer 26 if the orientation of input shaft 22is reversed), field shell 30, and armature 36. Magnetic flux flows frompole 72 of shell 30 across an air gap to pole 60 of rotor 28. Flux thentravels back and forth between disc 46 and armature 36 across the airgap between them. Flux then flows from disc 46 to hub 44 of rotor 28 andback to members 64, 66 of field shell 30.

In accordance with one aspect of the present invention, the location ofinner rotor pole 54 radially outwardly of inner field shell pole 68improves the magnetic efficiency of this magnetic circuit. Because fieldshell 30 is typically made from multiple members 64, 66, an air gapexists between members 64, 66. By locating inner pole 54 of rotor 28radially outwardly of inner pole 68 of field shell 30, at least some ofthe magnetic flux travels directly from pole 54 of rotor 28 to member 66of field shell 30 as shown in FIG. 2—bypassing the air gap betweenmembers 64, 66 of field shell 30. The relative location of the innerrotor and field shell poles 54, 68 is also advantageous because the gapbetween field shell poles 68, 72 is enlarged, enabling easier insertionand fastening of conduction assembly 32 within field shell 30.

In traveling between rotor 28 and field shell 30, magnetic flux travelsradially outwardly of bearing 50 along a path from rotor hub 44 tomembers 64, 66 of field shell 30. Magnetic flux also travels radiallyinwardly of bearing 50 along another path from rotor hub 44 to member 64of field shell 30. In this latter path, flux passes from hub 44 tospacer 82 (or spacer 26 if the orientation of input shaft 22 isreversed) before returning to member 64 of field shell 30. Thisalternate flux path allows a portion of the flux to avoid the highdensity area of inner rotor pole and field shell poles 54, 68 therebyimproving the magnetic efficiency of the circuit.

Shell 86 is provided to house conductor 84 and is also used to mountconductor 84 within field shell 30. Shell 86 may be molded fromconventional plastics. Shell 86 may include an integral terminalconnector 88 through which conductor 84 may be electrically connected toa power source. Connector 88 may extend through aperture 80 in fieldshell 30. Shell 86 may also define one or more lugs 90 sized to bereceived within recesses 76 in end wall 70 to prevent rotation ofconduction assembly 32.

Referring to FIG. 3, in accordance with another aspect of the presentinvention, shell 86 may include a radially outwardly extending flange92. Flange 92 is disposed proximate outer pole 72 of field shell 30.Flange 92 is affixed to field shell 30 at a plurality of points. Becauseconduction assembly 32 is affixed to field shell 30 proximate the outerdiameter of shell 30 rather than the inner diameter as in conventionaldevices, conduction assembly 32 can be secured in more locations and ata larger radius from the center of rotation 40 of device 20 as comparedto conventional devices. As a result, the structural integrity of device20 is greater than conventional devices. Further, the connection ofconduction assembly 32 proximate the outer diameter of shell 30 enablesthe novel arrangement of the inner rotor and field shell poles 54, 68for improved magnetic performance.

Flange 92 may be affixed to field shell 30 in a variety of ways. Asshown in FIG. 3, a radially inner surface of pole 72 of field shell 30(in particular shoulder 78) may be deformed at a plurality of pointsagainst flange 92 using a conventional tool to stake flange 92 withinfield shell 30. Referring to FIG. 4, in an alternative embodiment of theinvention, the radially inner surface of pole 72 may define a groove 94configured to receive a snap ring 96 that abuts and bears against flange92 to retain conduction assembly 32 in field shell 30. Referring to FIG.5, in another embodiment of the invention, fasteners 98 may extendthrough flange 92 into end wall 70 of field shell 30 at a plurality ofpoints to retain conduction assembly 32 within field shell 30. Referringto FIG. 6, in yet another embodiment of the invention, flange 92 may bedeformed by applying heat to portions of flange 92 to cause the heatedportions flange 92 to flow and extend into grooves 100 formed in pole 72and thereby stake flange 92 to shell 30. The flange 92 may also beaffixed to the field shell 30 using an adhesive on the surface of thefield shell 30 or within one or more grooves and may also be affixed bydefining a plurality of tabs in the flange 92 and locating the tabswithin corresponding slots in the field shell 30 upon a limited rotationof conduction assembly 32.

Referring again to FIGS. 1-2, brake plate 34 provides a braking surfacefor engagement by armature 36 to brake output member 24. Brake plate 34may be made from conventional materials having a relatively low magneticreluctance including conventional metals and metal alloys such as steel.Brake plate 34 extends about at least a portion of the circumference ofdevice 20 and is coupled to field shell 30. In particular, brake plate34 is coupled to flange 74 of field shell 30 using one or more fasteners102. Fasteners 102 may be made from non-magnetic materials or materialshaving a relatively high magnetic reluctance to reduce or eliminate fluxtransfer between brake plate 34 and field shell 30 and therebyfacilitate clutch engagement when conduction assembly 32 is energized.Brake plate 34 may be axially spaced from flange 74 of field shell 30using one or more spacers 104. Spacers 104 may include bores 106 throughwhich fasteners 102 extend. Spacers 104 may likewise be made fromnon-magnetic materials or materials having a relatively high magneticreluctance to reduce or eliminate flux transfer between brake plate 36and field shell 30. Referring to FIG. 1, brake plate 34 may include oneor more radially extending, acruately spaced tabs 108 divided byradially extending, arcuately spaced slots 110 formed in brake plate 34for a purpose described hereinbelow.

Armature 36 is provided to transmit a braking torque to output member 24and to selectively transmit a drive torque from rotor 28 to outputmember 24. Armature 36 may be made form a variety of conventional metalsand metal alloys including steel. Armature 36 is annular in constructionand disposed about axis 40. Armature 36 is axially spaced from rotor 28by an air gap. Like rotor disc 46, armature 36 includes a plurality ofradially spaced rows of angularly spaced slots 112 that facilitatetravel of magnetic flux back and forth between rotor 28 and armature 36upon energization of conduction assembly 32. In the illustratedembodiment, armature 36 includes two rows of slots 112. The radiallyinner row of slots 112 on armature 36 is disposed between the radiallyinner and radially center row of slots 58 on rotor disc 46. The radiallyouter row of slots 112 on armature 36 is disposed between the radiallycenter and radially outer rows of slots 58 on disc 46. It should beunderstood that the number of rows of slots 112 on armature 36, thenumber of slots 112 in any one row, and the size and shape of slots 112may vary. Armature 36 is coupled to output member 24. In particular,armature 36 may be coupled to output member 24 by a plurality of leafsprings 114 Springs 114 transmit drive and braking torque from armature36 to output member 24 and allow for axial movement of armature 36relative to member 24 and towards and away from rotor disc 46. Springs114 may be made from stainless steel and are connected at one end toarmature 36 and at an opposite end to output member 24 usingconventional fasteners 116 such as rivets, screws, bolts, or pins.

Magnets 38 are provided to create a magnetic circuit between brake plate34 and armature 36 to draw armature 36 into engagement with brake plate34 and provide a braking torque to output member 24. Magnets 38 maycomprise neodymium iron boron (Nd—Fe—B) magnets or other known permanentmagnets. Referring to FIG. 2, magnets 38 may be embedded within a closedbore 118 in brake plate 34 and may be arranged such that one face of themagnet 38 is flush with one side (and the engagement surface) of brakeplate 34. By placing the magnets 38 such that one face is flush with theengagement surface of brake plate 34, magnets 38 add to the wear surfaceof brake plate 34 increasing its wear resistance and the brakingsurface. Referring to FIG. 1, magnets 38 may be arcuately spaced fromone another about the circumferential extent of brake plate 34. A singlemagnet 38 may be disposed in each tab 108 wherein slots 110 serve tomagnetically isolate each magnet 38 from other magnets 38.Alternatively, more than one magnet 38 may be disposed in a single tab108 (and/or slots 110 eliminated) provided that the magnets 38 areappropriately spaced from one another. Magnets 38 may also be disposedin every other tab 108 to increase wear surface. It will further beappreciated that the number and location of magnets 38 within brakeplate 34 may vary depending upon the characteristics of device 20 andrelated design requirements. As illustrated, magnets 38 are arrangedsuch that the facing poles of adjacent magnets are of like polaritythereby forming parallel magnetic circuits. Alternatively, magnets 38may be arranged such that the facing poles of adjacent magnets 38 are ofopposite polarity thereby forming a less efficient series magneticcircuit.

Referring again to FIG. 2, in accordance with the present invention,magnets 38 are axially aligned with a portion of armature 36. Referringto FIG. 7, magnets 38 are oriented such that magnetic flux travelsaxially through said magnets 38. In particular, magnetic flux travelsthrough one pole of each magnet 38 (located at the radial center ofmagnet 38) into brake plate 34. Flux continues to travel radiallyinwardly and outwardly along brake plate 34 towards an opposite pole ofeach magnet 38 (located at the radial periphery of magnet 38). Flux thentravels to armature 36 and radially inwardly and outwardly and arcuatelyalong armature 36 before crossing back into the radially center pole ofmagnet 38. The magnetic circuit formed by the inventive device 20 ismore efficient than in conventional devices. In particular, the locationof magnets 38 reduces the number of air gaps within the magnetic circuitformed by the brake plate 34, magnet 38, and armature 36 therebyimproving the efficiency of the magnetic circuit. In particular,magnetic flux crosses only three air gaps: (i) from magnet 38 to brakeplate 34; (ii) from brake plate 34 to armature 36; and (iii) fromarmature 36 to magnet 38. Further, because two of the air gaps involvethe armature 36 and the braking surface formed by brake plate 34 ormagnets 38, magnetic attraction is enhanced. The location of magnets 38(i.e., remote from field shell 30) and resulting magnetic circuit alsoreduces flux travel between brake plate 34 and field shell 30 therebyenabling easier release of armature 36 from the brake plate 34 duringclutch engagement.

Referring now to FIGS. 8-9, a device 200 in accordance with anotherembodiment of the present invention is illustrated. Device 200 issubstantially similar to device 20 and reference may be had to thedescription above for like components. Device 200 differs from device 20in that magnets 38 are disposed within armature 202 rather than brakeplate 204. Locating magnets 38 with armature 202 as opposed to brakeplate 204 enables greater wear surface and wear resistance in brakeplate 204 relative to brake plate 34 of device 20 (because of theabsence of recessed magnets 38 and slots 110). Further, the magneticflux within the magnetic brake circuit can be balanced with the fluxgenerated upon energization of conduction assembly 32 to improve clutchengagement performance. On the other hand, more magnets 38 may berequired and the magnets 38 are subjected to more extreme operatingconditions. Referring to FIG. 9, magnets 38 may be embedded withinclosed bores 206 in armature 202 and may be arranged such that one faceof the magnet 38 is flush with the side (and engagement surface) ofarmature 202. By placing the magnets 38 such that one face is flush withthe engagement surface of armature 202, magnets 38 add to the wearsurface of armature 202 increasing its wear resistance and the brakingsurface. Referring to FIG. 8, magnets 38 may be arcuately spaced fromone another about the circumferential extent of armature 202. Armature202 may include one or more radially extending, acruately spaced tabs208 about its radially outer periphery divided by radially extending,arcuately spaced slots 210 formed in armature 202 for a purposedescribed hereinbelow. A single magnet 38 may be disposed in each tab208 wherein slots 210 serve to magnetically isolate each magnet 38 fromother magnets 38. Alternatively, more than one magnet 38 may be disposedin a single tab 208 (and/or slots 210 eliminated) provided that themagnets 38 are appropriately spaced from one another. Magnets 38 mayalso be disposed in every other tab 208 to increase wear surface. Itwill further be appreciated that the number and location of magnets 38within armature 202 may vary depending upon the characteristics ofdevice 200 and related design requirements. As illustrated, magnets 38are again arranged such that the facing poles of adjacent magnets are oflike polarity thereby forming parallel magnetic circuits. Alternatively,magnets 38 may be arranged such that the facing poles of adjacentmagnets 38 are of opposite polarity thereby forming a less efficientseries magnetic circuit.

Referring again to FIG. 9, in accordance with the present invention,magnets 38 are axially aligned with a portion of brake plate 204.Magnets 38 are again oriented such that magnetic flux travels axiallythrough said magnets 38. In particular, magnetic flux travels throughone pole of each magnet 38 (located at the radial center of magnet 38)into armature 202. Flux continues to travel radially inwardly andoutwardly and arcuately along armature 202 towards an opposite pole ofeach magnet 38 (located at the radial periphery of magnet 38). Flux thentravels to brake plate 204 and radially inwardly and outwardly andarcuately along brake plate 204 before crossing back into the radiallycenter pole of magnet 38. The magnetic circuit formed by the inventivedevice 200 is again more efficient than in conventional devices becausemagnetic flux crosses only three air gaps: (i) from magnet 38 toarmature 202; (ii) from armature 202 to brake plate 204; and (iii) frombrake plate 204 to magnet 38. Further, because two of the air gapsinvolve the brake plate 204 and the braking surface formed by armature202 or magnets 38, magnetic attraction is enhanced. The location ofmagnets 38 (i.e., remote from field shell 30) and resulting magneticcircuit also again reduces flux travel between brake plate 204 and fieldshell 30 thereby enabling easier release of armature 202 from the brakeplate 204 during clutch engagement.

Referring now to FIG. 10-11, a device 300 in accordance with anotherembodiment of the present invention is illustrated. Device 300 issubstantially similar to devices 20, 200 and reference may be had to thedescription above for like components. Device 300 differs from devices20, 200 in that magnets 302 are oriented in a different manner withinbrake plate 304 or armature 306. In the illustrate embodiment magnets302 are disposed within brake plate 304. It should be understood,however, that magnets 302 could alternatively be disposed withinarmature 306 as described hereinabove with reference to FIGS. 8-9.Referring to FIG. 10, magnets 302 are oriented with its opposite polesarcuately spaced from one another. Referring to FIG. 11, magnets 302 maybe embedded within through bores 308 in brake plate 304 (or armature306) and may be arranged such that one face of the magnet 302 is flushwith one side (and the engagement surface) of brake plate 304 (orarmature 306). By placing the magnets 302 such that one face is flushwith the engagement surface of brake plate 304 (or armature 306),magnets 302 add to the wear surface of brake plate 304 (or armature 306)increasing its wear resistance and the braking surface. Referring againto FIG. 10, magnets 302 may be arcuately spaced from one another aboutthe circumferential extent of brake plate 304 (or armature 306). Brakeplate 304 may again include one or more radially extending, acruatelyspaced tabs 310 divided by radially extending, arcuately spaced slots312. A single magnet 302 may again be disposed in each tab 310 of brakeplate 304 (or armature 306) wherein slots 312 serve to magneticallyisolate each magnet 302 from other magnets 302. Alternatively, more thanone magnet 302 may again be disposed in a single tab 310 (and/or slots312 eliminated) provided that the magnets 302 are appropriately spacedfrom one another. Magnets 302 may also be disposed in every other tab310 to improve wear resistance. It will further be appreciated that thenumber and location of magnets 302 within brake plate 304 (or armature306) may vary depending upon the characteristics of device 300 andrelated design requirements. As illustrated, magnets 302 are againarranged such that the facing poles of adjacent magnets are of likepolarity thereby forming parallel magnetic circuits. Alternatively,magnets 302 may be arranged such that the facing poles of adjacentmagnets 302 are of opposite polarity thereby forming a less efficientseries magnetic circuit.

Referring to FIG. 11, in accordance with the present invention, magnets302 are again axially aligned with a portion of armature 306 (or brakeplate 304). Magnets 302 are oriented such that magnetic flux travelsarcuately through magnets 302. In particular, magnetic flux travels fromone pole of each magnet 302 (located at one arcuate end of magnet 302)into brake plate 304 (or armature 306). Flux then travels to armature306 (or brake plate 304) across the air gap between brake plate 304 andarmature 306. Flux continues arcuately across armature 306 (or brakeplate 304) and returns to brake plate 304 (or armature 306) across thesame air gap before returning to the opposite pole of magnet 302(located at the other arcuate end of magnet 302) from brake plate 304(or armature 306). The magnetic circuit formed by the inventive device300 is again more efficient than in conventional devices (although lessso than the magnetic circuit in devices 20, 200). In particular, thelocation of magnets 302 reduces the number of air gaps within themagnetic circuit formed by the brake plate 304, magnet 302, and armature306 thereby improving the efficiency of the magnetic circuit. Inparticular, magnetic flux crosses only four air gaps: (i) from magnet302 to brake plate 304 (or armature 306); (ii) from brake plate 304 toarmature 306 (or from armature 306 to brake plate 304); (iii) fromarmature 306 to brake plate 304 (or from brake plate 304 to armature306); and (iv) from brake plate 304 (or armature 306) back into magnet302. Further, because two of the air gaps involve the armature 306 andthe braking surface formed by brake plate 304, magnetic attraction isenhanced. The location of magnets 302 (i.e., remote from field shell 30)and resulting magnetic circuit also reduces flux travel between brakeplate 304 and field shell 30 thereby enabling easier release of armature306 from the brake plate 304 during clutch engagement.

Referring now to FIG. 12 a device 400 in accordance with anotherembodiment of the present invention is illustrated. Device 400 issubstantially similar to devices 20, 200, 300 and reference may be hadto the description above for like components. Device 400 differs fromdevices 20, 200, 300 in that magnets 402 are oriented in a differentmanner within brake plate 404 or armature 406. In the illustratedembodiment magnets 402 are again disposed within brake plate 404. Itshould again be understood, however, that magnets 402 couldalternatively be disposed within armature 406 as described hereinabovewith reference to FIGS. 8-9. Magnets 402 are oriented with oppositepoles radially spaced from one another. Magnets 402 may again beembedded within through bores 408 in brake plate 404 (or armature 406)and may be arranged such that one face of the magnet 402 is flush withone side (and the engagement surface) of brake plate 404 (or armature406). By placing the magnets 402 such that one face is flush with theengagement surface of brake plate 404 (or armature 406), magnets 402 addto the wear surface of brake plate 404 (or armature 406) increasing itswear resistance and the braking surface. As in devices 20, 200, and 300,magnets 402 may be arcuately spaced from one another about thecircumferential extent of brake plate 404 or armature 406 in a mannersimilar to that described hereinabove with reference to devices 20, 200and 300.

In accordance with the present invention, magnets 402 are again axiallyaligned with a portion of armature 406 (or brake plate 404). Magnets 402are oriented such that magnetic flux travels radially through magnets402. In particular, magnetic flux travels from one pole of each magnet402 (located at one radial end of magnet 402) into brake plate 404 (orarmature 406). Flux then travels to armature 406 (or brake plate 404)across the air gap between brake plate 404 and armature 406. Fluxcontinues radially through armature 406 (or brake plate 404) and returnsto brake plate 404 (or armature 406) across the same air gap beforereturning to the opposite pole of magnet 402 (located at the otherradial end of magnet 402) from brake plate 404 (or armature 406). Themagnetic circuit formed by the inventive device 400 is again moreefficient than in conventional devices (although less so than themagnetic circuit in devices 20, 200). In particular, the location ofmagnets 402 reduces the number of air gaps within the magnetic circuitformed by the brake plate 404, magnet 402, and armature 406 therebyimproving the efficiency of the magnetic circuit. In particular,magnetic flux again crosses only four air gaps: (i) from magnet 402 tobrake plate 404 (or armature 406); (ii) from brake plate 404 to armature406 (or from armature 406 to brake plate 404); (iii) from armature 406to brake plate 404 (or from brake plate 404 to armature 406); and (iv)from brake plate 404 (or armature 406) back into magnet 402. Further,because two of the air gaps involve the armature 406 and the brakingsurface formed by brake plate 404, magnetic attraction is enhanced. Thelocation of magnets 402 (i.e., remote from field shell 30) and resultingmagnetic circuit also reduces flux travel between brake plate 404 andfield shell 30 thereby enabling easier release of armature 406 from thebrake plate 404 during clutch engagement.

While the invention has been shown and described with reference to oneor more particular embodiments thereof, it will be understood by thoseof skill in the art that various changes and modifications can be madewithout departing from the spirit and scope of the invention.

1. A rotational coupling device, comprising: a rotor coupled to an inputshaft for rotation therewith, said input shaft disposed about arotational axis; a field shell disposed about said input shaft and fixedagainst rotation, said field shell defining axially extending, radiallyspaced inner and outer poles and an end wall extending radially betweensaid inner and outer poles, an electrical conduction assembly disposedwithin said field shell between said inner and outer poles and on afirst side of said rotor, said assembly including a conductor disposedwithin a shell, said shell including a radially outwardly extendingflange disposed proximate said outer pole of said field shell and saidend wall; and an armature disposed axially between said rotor and abrake plate on a second side of said rotor opposite said conductor, saidarmature coupled to an output member wherein said flange is affixed toat least one of said outer pole and said end wall of said field shell ata plurality of points located further outward radially than an outerdiameter of said conductor by a plurality of fasteners, each of saidplurality of fasteners extending through said flange and into said fieldshell at one of said plurality of points and each of said fastenershaving a head abutting a first side of said flange opposite a secondside of said flange facing said field shell.
 2. The rotational couplingdevice of claim 1 wherein said brake plate is coupled to said fieldshell and, further comprising a first permanent magnet coupled to one ofsaid brake plate and said armature and axially aligned with a firstportion of the other of said brake plate and said armature along an axisextending parallel to said rotational axis, said first permanent magnetembedded within a bore formed in said one of said brake plate and saidarmature.
 3. The rotational coupling device of claim 1 wherein saidrotor defines axially extending, radially spaced inner and outer poles,said inner pole of said rotor disposed radially outwardly of said innerpole of said field shell.
 4. A rotational coupling device, comprising: arotor coupled to an input shaft for rotation therewith, said input shaftdisposed about a rotational axis; a field shell disposed about saidinput shaft and fixed against rotation, said field shell definingaxially extending, radially spaced inner and outer poles and an end wallextending radially between said inner and outer poles, an electricalconduction assembly disposed within said field shell between said innerand outer poles and on a first side of said rotor, said assemblyincluding a conductor disposed within a shell, said shell including aradially outwardly extending flange disposed proximate said outer poleof said field shell and said end wall; and an armature disposed axiallybetween said rotor and a brake plate on a second side of said rotoropposite said conductor, said armature coupled to an output memberwherein said flange is affixed to at least one of said outer pole andsaid end wall of said field shell at a plurality of points locatedfurther outward radially than an outer diameter of said conductorwherein a radially inner surface of said outer pole of said field shellis deformed against said flange at each of said plurality of points. 5.A rotational coupling device, comprising: a rotor coupled to an inputshaft for rotation therewith, said input shaft disposed about arotational axis; a field shell disposed about said input shaft and fixedagainst rotation, said field shell defining axially extending, radiallyspaced inner and outer poles and an end wall extending radially betweensaid inner and outer poles, an electrical conduction assembly disposedwithin said field shell between said inner and outer poles and on afirst side of said rotor, said assembly including a conductor disposedwithin a shell, said shell including a radially outwardly extendingflange disposed proximate said outer pole of said field shell and saidend wall; and an armature disposed axially between said rotor and abrake plate on a second side of said rotor opposite said conductor, saidarmature coupled to an output member wherein said flange is affixed toat least one of said outer pole and said end wall of said field shell ata plurality of points located further outward radially than an outerdiameter of said conductor further comprising a snap ring disposedwithin a groove formed in a radially inner surface of said outer pole ofsaid field shell and abutting said flange.
 6. A rotational couplingdevice, comprising: a rotor coupled to an input shaft for rotationtherewith, said input shaft disposed about a rotational axis; a fieldshell disposed about said input shaft and fixed against rotation, saidfield shell defining axially extending, radially spaced inner and outerpoles and an end wall extending radially between said inner and outerpoles, an electrical conduction assembly disposed within said fieldshell between said inner and outer poles and on a first side of saidrotor, said assembly including a conductor disposed within a shell, saidshell including a radially outwardly extending flange disposed proximatesaid outer pole of said field shell and said end wall; and an armaturedisposed axially between said rotor and a brake plate on a second sideof said rotor opposite said conductor, said armature coupled to anoutput member wherein said flange is affixed to at least one of saidouter pole and said end wall of said field shell at a plurality ofpoints located further outward radially than an outer diameter of saidconductor wherein said flange extends into a groove formed in said fieldshell.
 7. The rotational coupling device of claim 6 wherein said grooveis formed in a radially inner surface of said outer pole of said fieldshell.
 8. A rotational coupling device, comprising: a rotor coupled toan input shaft for rotation therewith, said input shaft disposed about arotational axis; a field shell disposed about said input shaft and fixedagainst rotation, said field shell defining axially extending, radiallyspaced inner and outer poles and an end wall extending radially betweensaid inner and outer poles, an electrical conduction assembly disposedwithin said field shell between said inner and outer poles and on afirst side of said rotor, said assembly including a conductor disposedwithin a shell, said shell including a radially outwardly extendingflange disposed proximate said outer pole of said field shell and saidend wall; and an armature disposed axially between said rotor and abrake plate on a second side of said rotor opposite said conductor, saidarmature coupled to an output member wherein said flange is affixed toat least one of said outer pole and said end wall of said field shell ata plurality of points located further outward radially than an outerdiameter of said conductor wherein said field shell defines a recess andsaid shell defines an axially extending lug configured to be receivedwithin said recess.